1. Field of the Invention
This invention relates to a method for the breeding of bivalves (specifically giant scallops, Placopecten sp.).
2. Description of the Prior Art
The giant scallop (Placopecten magellanicus) has been identified as a promising aquaculture candidate species. The development of an aquaculture industry with scallops depends on a supply of "seed" or settling "spat" (i.e. young scallops leaving their pelagic larval stage to become benthic or bottom dwellers). Two potential supply lines exist, hatchery production and collection of wild seed. Until recently, hatchery production has not been successful at any meaningful scale, and collection of wild seed has been quite variable from year to year. The present status is that neither supply route has demonstrated the reliability necessary to sustain a culture industry.
Oysters, mussels, clams, scallops and the like are referred to as bivalves, and the commercial farming of such bivalves is referred to as bivalve culture. All bivalves have a similar life cycle. Initially, the bivalve larvae are free swimming ("planktonic"). After a time, the planktonic larvae develop into a stage capable of crawling referred to as pediveliger. Pediveligers which are capable of attaching to a substrate (referred to as "settling") are said to be competent. After setting on a substrate, (referred to as "cultch"), the larvae are allowed to develop and are finally harvested when they reach a suitable size.
Natural spawning of mature scallops results first in the development of the embryo. The embryo develops to the larvae stage, where larvae grow to the major stage of metamorphosis in their life cycle known as settlement. Larvae in this phase (30-40 days old) are free swimming or planktonic (spawn). At the settlement stage in their life cycle, planktonic larvae undergo a metamorphosis and develop into juvenile scallops (spat) which are essentially miniature adults. They measure approximately 0.5 mm in shell height. The spat then develop through the juvenile stage to the mature adult stage.
Breeding of giant scallop under controlled conditions and the consistent production of spat is highly desirable as a step towards aquaculture of this species. In the wild, the spawn settles widely on broad expanses of ocean bottom in waters from 10-100 m deep. Thus settling of the scallop spawn in the wild is impractical, often unpredictable.
For example, U.S. Pat. No. 3,196,833 patented Jul. 27, 1965 by J. B. Glancy purports to relate to a method of producing shellfish seed, e.g. the seed of oysters, clams, mussels, and scallops; in reality the patentee merely teaches a method for oyster "farming". Briefly, the method contemplates that natural oyster growing water, e.g. bay water, may be used during the production of oyster seed by controlling the toxicity of the water and by maintaining the water under conditions which provide for an adequate content of natural oyster food within the water itself. In order to accomplish this, the oyster seed production is carried on in tanks or other vessels located within the confines of a "greenhouse" type of solar radiation-admitting enclosure. The natural oyster growing water employed in the tanks in the greenhouse is treated by centrifuging to removing silt and the natural marine enemies of the oyster larvae without removing the relatively lighter natural oyster food, e.g. plankton, which is present in the water.
The process starts by collecting spawn from selected strains of oysters and fertilizing the eggs by the addition of sperm in accordance with known techniques. After fertilization, when the oyster embryos or larvae begin to swim, they are transferred to larval tanks wherein the swimming larvae are cultivated until they reach settling size. During the larval period, the treated water in the tanks is changed daily, or more often, to provide the necessary supply of food for the larvae and to minimize the toxic level of the water. When the larvae grow to a settling size, they are ready for settling and are transferred to settling tanks located within the greenhouse. Mesh bags filled with cultch, e.g. bare mollusc shells, are placed in the settling tanks with the larvae and the tanks supplied with treated water, so that the larvae attach themselves to the cultch where they become known as "set" or "spat". When the setting concentration reaches a suitable level, the cultch with attached oyster set is taken from the setting tanks and transferred to a protected area of the natural oyster growing grounds. Since the oyster set are still of a relatively small size, the bags of cultch are suspended from floats or other support devices in the protected area of the oyster growing grounds to protect the spat from natural marine enemies and adverse water conditions. Finally, when the suspended spat or set reach a larger size, they are removed from the suspension devices and the cultch shells are then spread on the natural oyster growing grounds for cultivation to market size in accordance with known techniques.
The invention also teaches the resetting of oyster set which have set on the inner surfaces or walls of the setting tanks rather than on the cultch material. This is accomplished by brushing the walls of the setting tanks to remove the set and then recovering the removed set by means of screening. The brushed-off oyster set is then sprinkled at a desired concentration on cultch material in resetting tanks, where the set resets itself within a period of about four days. The cultch having the reset spat is then transferred to the protected area of the natural growing grounds in the same manner as the cultch from the setting tanks.
U.S. Pat. No. 4,080,930 patented Mar. 28, 1978 by G. D. Pruder et al provided a method for rearing commercially desirable bivalve molluscs, e.g. oysters, clams, mussels, and scallops under artificial conditions to any marketable size in substantially reduced time periods. In practice, however, the patent is related to the rearing of oysters. Oyster spat produced by known means are placed in growing tanks and fed at certain regular times with certain species of algae in unusually large quantities, at unusually high algae cell concentrations, and maintained at unusually high temperatures until oysters reach the desired size. The tanks and oysters are meticulously cleansed and seawater or other source of salts and minerals is added at regular times during the rearing period.
Canadian Patent 1,112,113 patented Nov. 10, 1981 by J. B. Marliave provided an apparatus for the field rearing of planktonic larval forms of marine animals involving the suspension of a field culture chamber in oceanic tidal waters. The chamber was provided with an entry port in its side for adjustably admitting tidal flow water, a means for deflecting water around the chamber periphery, and an exit port in the chamber bottom to permit the outflow of water from the chamber. A curtain was suspended over the interior openings of the entry vanes to prevent the exit of larvae through the entry port. The interior of the chamber was stocked with larvae of a preselected species of marine animal. The chamber was oriented in response to the tidal flow of water so that the water flowed into the chamber through the entry port. Prior to entering the chamber, the water was screened to prevent admittance of plankton of greater than a predetermined size and to permit admittance of plankton small enough to be utilized as food by the larvae of the preselected species. Water flowing out of the chamber through the exit port was filtered to prevent the escape of larvae and food plankton.
Canadian Patent 1,132,408 patented Sep. 28, 1982 by G. S. Lockwood et al provided a process of culturing gastropod molluscs and other benthic motile marine and aquatic animals from the larval stage through infancy in a body of water in a growing tank having therein settlement surfaces upon which the larvae settle and in which the animals resulting from larvae metamorphosis live. The process included conditioning the settlement surfaces to develop thereon a microbiological community so as to induce settlement of larvae and to support life thereon; then introducing larvae of the animal into the tank whereby at least a portion of the larvae will settle upon the settlement surfaces and undergo metamorphosis and subsequent growth; then circulating water in the tank at least periodically; and finally controlling the biological and chemical balance in the tank to provide food and to limit the build-up of harmful components and conditions in the tank.
Canadian Patent 1,136,933 patented Dec. 7, 1982 by P. C. Brinkworth provided a method of cultivating marine and aquatic species. The species were housed in habitats in which they remained for the major part of their growth cycle, such habitats being located within a body of water. Clean water from an external source was passed through at least one restricted passage means into each habitat to provide a compatible zone within each habitat for the specie contained therein. Water from that restricted passage means flowed past the species in laminar flow condition to an incompatible zone external to each habitat. Each adjacent wall of each habitat was formed of imperforate material so that the species contained within each habitat was isolated from each other and so that cross-contamination cannot take place.
U.S. Pat. No. 4,198,926 patented Apr. 12, 1988 by D. E. Morse provided a method to induce and control spawning and reproduction in shellfish in seawater, which comprised adding, to the seawater, an oxidizing agent which yields activated oxygen, particularly hydrogen peroxide. The patent found that the addition of low concentrations of such oxidizing agent, particularly hydrogen peroxide, to alkaline seawater will cause synchronous spawning of gravid male and female species of shellfish, e.g. abalones, mussels, scallops and oysters.
U.S. Pat. No. 4,348,983 patented Sep. 14, 1982 by K. L. Cooper provided a method for inducing the setting of planktonic bivalves onto a substrate is disclosed. Planktonic bivalves which have reached the competent pediveliger stage, are exposed to certain 1-substituted-3,4-dihydroxylbenzenes, e.g. 3,4-dihydroxyphenylalanine at a sufficient minimum concentration.
U.S. Pat. No. 3,996,895 patented Dec. 14, 1976 by J. C. Wiegardt, Jr. provided a system for the artificial growing of dense populations of hatchery-derived filter-feeding shellfish, e.g. free oysters and clams, with means provided for holding these populations in currents of nutrient-laden water. These means involved a flume system for growing the seed from hatchery sizes to intermediate sizes, with a special case for growing hardshell clams toward maturity in a flume, or "spillway" system. As the seed grew toward maturity, their requirements for current and for nutrients increased. In the patented system, a progression of structures was utilized, beginning with a basic raft structure and adding channelling extensions to this primary structure. Each addition to the primary structure was designed to increase the efficiency of the system in utilizing a basic current and phytoplankton resource. The system was capable of taking tiny hatchery-derived seed and growing them to commercial maturity in a series of stages designed to optimize handling and feeding requirements at the various stages. At the stages where the organisms approached commercial maturity and required current flow and more nutrients, the system was capable of developing an increased level of efficiency in regard to the utilization of resources of current flow and nutrients. At its most efficient level, the system contemplates harvest of a phytoplankton resource of any esturial area at optimum sustainable levels.